Aerodynamic engineers have long desired to measure high frequency flow and pressure disturbances in gas turbine engines and aircraft wings. The capability was made possible with extremely compact pressure transducers fabricated from micro-machined silicon. The frequencies of concern were for example, in the tens of thousands of kilohertz (kHz). As such, Kulite Semiconductor Products, Inc., the assignee herein, has developed many transducers which operate to measure such pressure disturbances in gas turbine engines and aircraft wings. Such devices are the subject matter of various patents that describe their operation and fabrication. See, for example, U.S. Pat. No. 6,612,178 entitled “Leadless Metal Media Protected Pressure Sensor” issued on Sep. 2, 2003 to A. D. Kurtz et al. and assigned to the assignee herein. See also, U.S. Pat. No. 6,363,792 entitled “Ultra High Temperature Transducer Structure” issued on Apr. 2, 2002 to A. D. Kurtz et al. and assigned to the assignee herein. In any event, as will be explained, there are certain situations where mounting of the transducer becomes extremely difficult.
For example, in order to determine the pressure and high frequency flow in gas turbines, a recessed pipe is attached to the combustion chamber that allows the hot gasses within the chamber to cool before reaching the sensor. While the pipe does successfully cool the gases, it also reduces measurement of bandwidth because of the generation of harmonic frequencies. Similar to blowing air over an open bottle top, the air inside the recessed pipe will be compressed by the air jet back out of the recess. In essence, the air inside the bottle acts as a spring. The oscillations of the air inside the recess results in a resonant frequency similar to that of an organ pipe. Such vibrations make measuring the pressure and flow of the gases within the combustion chamber of the gas turbine difficult. As will be explained, in the prior art, a long, curled tube (or “infinite tube”) of decreasing diameter has been used to remove such resonances. However, such a solution requires many feet of tubing and very accurate coiling of the tube. Further difficulties associated with the prior art include the lack of access for mounting such transducers in a turbine case, as well as problems which involve discriminating against low and high frequencies.
An alternative mechanism that overcomes one or more of these problems is desirable.